The present invention relates to a process for preparing gelled overbased materials and to lubricants and other substances containing such gelled overbased materials.
Overbased materials have been long known and are important lubricating oil additives. These materials are metal salts of acidic organic compounds. Overbased materials are single phase, homogeneous, and generally apparently Newtonian systems characterized by a metal content in excess of that which would be present according to the stoichiometry of the metal and the particular acidic organic compound reacted with the metal. Overbased materials can be converted from their original Newtonian form to a gelled form by a variety of treatments, some of which are set forth in certain of the following documents:
U.S. Pat. No. 3,242,079, McMillen, discloses a grease prepared by mixing mineral oil, a carbonated, basic alkaline earth metal salt of an acid of at least 12 carbon atoms, and an active hydrogen compound such as a lower aliphatic carboxylic acid, water, or water-alcohol mixtures. Addition of acetic acid and mineral oil to overbased calcium petroleum sulfonate and heating to 100.degree.-150.degree. C. for about 9 hours forms a grease. Examples illustrate the use of alcohol/water to effect the grease formation.
U.S. Pat. No. 3,492,231, McMillen, discloses preparation of a non-Newtonian disperse system. The conversion agents include lower aliphatic carboxylic acids, water, aliphatic alcohols, cycloaliphatic alcohols, phenols, ketones, aldehydes, amines, boron acids, phosphorus acids, and carbon dioxide. Mixtures of two or more of these conversion agents are also useful. The use of a mixture of water and one or more of the alcohols is especially effective.
U.S. Pat. No. 3,766,066, McMillen, discloses a process for preparing solid, metal-containing compositions by isolating the solid from a gelled overbased material.
U.S. Pat. No. 4,597,880, Eliades, discloses a 1-step process for making overbased calcium sulfonate greases, comprising introducing into a reactor a solution of a sulfonic acid having an aliphatic chain of at least 12 carbon atoms; calcium oxide and/or calcium hydroxide; minor proportions of (a) water-soluble carboxylic acids such as, for example, acetic acid; (b) aliphatic alcohols or alkoxyalkanols, such as methyl alcohol or methyl cellosolve; and (c) water, prior to carrying out a carbonation step.
U.S. Pat. No. 3,730,895, Kjonaas, discloses a calcium overbased carboxylate. Example 6 shows the preparation of a concentrate composition using a dispersant comprising a combination of carboxylates overbased with calcium carbonate. Glacial acetic acid and 12-hydroxystearic acid are employed. The product has the appearance of a grease. The concentrate was blended with a lithium soap based grease composition.
The present invention provides an improved method for converting a Newtonian overbased material to a gel. The present invention further provides a method for preparing certain of the Newtonian overbased materials which are suitable for subsequent conversion to gels. Gels prepared from overbased saturated carboxylates often show improved thickening efficiency and utility in greases, paints, and other applications, compared to gels prepared from unsaturated carboxylates or other overbased materials in general. But the process for preparing such gelled overbased saturated carboxylates or their equivalents is generally quite difficult. The initial overbasing of saturated carboxylic acids is complicated. While one might overbase such acids in a higher alcohol Carrier solvent such as isooctyl alcohol at 150.degree.-160.degree. C., removing the water of reaction as it is formed, such a process would have disadvantages. For example, a relatively high temperature is required, and the product is formed in an alcohol solvent, which may be undesirable. Alternatively, one might attempt to use an aromatic carrier such as toluene, mixed xylenes, or higher aromatics, conducting the overbasing reaction at 50.degree.-55.degree. C. In such a process the mixture tends to solidify during the overbasing, even with extreme dilution with the carrier solvent, thus preventing effective preparation of the overbased material. Thus by this second possible route overbased coconut oil can be prepared, but only with difficulty, yielding a solid product even at 21% concentration. And overbased stearic, palmitic, or 12-hydroxystearic acids cannot generally be prepared by this route at all, whether the starting material be the acid, ester, or triglyceride. The gelation of such overbased carboxylic acids, once they are prepared, is likewise difficult and slow, often requiring treatment for several hours at elevated temperature even in the presence of a conversion agent.